Lubricant

ABSTRACT

A lubricant containing one or more compounds selected from the keto compounds of general formula 1 
     
       
         
         
             
             
         
       
     
     in which R 1 , R 2  and X have the indicated significance.

BACKGROUND OF THE INVENTION

This invention relates to lubricants containing mesogenic compounds.

Lubricants which contain mesogenic compounds have long been known (EP 0330 068). It is assumed that a mesophase, that is to say a nematic,smectic or discotic liquid-crystalline phase, can be induced therein byincreasing the pressure or by a lubricating action in machine bearings.Such phases which are formed by compounds with elongated bar-shaped ordiscoid molecules are generally known (H Kelker, R Hatz, Handbook ofLiquid Crystals, Verlag Chemie, Weinheim 1980). Such phase transitionsmake it possible to avoid in particular in the lubrication gap of plainbearings contacts between the solid bodies which are moving relative toeach other. In comparison with conventional lubricants it is possibletherewith to achieve an enormous reduction in frictional losses. Thus,under conditions at which coefficients of friction of between 0.2 and0.1 (typical of mixed friction) were found, coefficients of friction of<0.005 were measured, which are typical for plain bearings operated inthe hydrodynamic range (R Eidenschink, Mol. Cryst. Liq. Cryst. 461,71-81 (2007) and literature quoted therein).

The lubricants which have been known hitherto and which containsubstances with liquid-crystalline properties must be produced in anexpensive and complicated procedure and with high losses in respect ofmaterials used. Hitherto therefore they could only be used for thelubrication of highly problematical bearings.

BRIEF SUMMARY OF THE INVENTION

The invention concerns a lubricant containing between 20 and 99.9% bymass of one or more compounds of the general formula 1

wherein

X denotes H, F, Cl, —CH₃, —C₂H₅, —OCH₃, R₁ respectively denoteindependently of each other H, an alkyl residue having a total ofbetween 1 and 18 C-atoms, in which also one or two non-adjacent CH₂groups can be replaced by —O—, —S— or —CO— and two adjacent CH₂ groupscan be replaced by —COO— or —OOC—,

R₂ respectively denote independently of each other an alkyl residuehaving a total of between 1 and 18 C-atoms, in which also one or twonon-adjacent CH₂ groups can be replaced by —O—, —S— and two non-adjacentCH₂ groups can be replaced by —COO— or —OOC—, or the residue

with the above-specified significances for X and R₁ and wherein n is anumber between zero and 12 and q is zero or 1,

and machine bearings lubricated therewith.

DETAILED DESCRIPTION OF THE INVENTION

The object of the present invention was to find the lubricant which canbe economically produced from inexpensive starting materials and whichnonetheless permits particularly low coefficients of friction incomparison with conventional lubricants, in particular in plainbearings. The compounds of formula 1 above have admittedly been recordedby a Markus formula of an earlier invention (DE 38 10 626) but becauseof the low ratio of length and diameter of their molecules noliquid-crystalline properties can be assumed by the man skilled in theart, and also a liquid-crystalline phase was never observed in suchcompounds.

Surprisingly however particularly low coefficients of friction can beachieved in machine bearings by the lubricant according to theinvention. An above-indicated phase transition which is induced byshearing actions in the lubrication gap of a bearing is responsible forthat surprising effect, in spite of the disadvantageous geometry of themolecules of the compounds of formula 1. It is however also possiblethat there is an unknown cause in that respect.

The compounds of the general formula 1 can advantageously be produced bya single synthesis step from inexpensive compounds. For that purpose anacetophenone which is dissolved in a carboxylic acid ester can becondensed under the effect of sodium (see DE 29 18 775, synthesisdiagram 1).

With the same reaction implementation, starting from an acetophenone anda dicarboxylic acid ester, compounds of formula 1 are also obtained(synthesis diagram 2).

The β-benzoyl carboxylic acid esters also embraced by the invention (seeK Matsuki et al, Chem. Pharm. Bull 41, 643 (1993), synthesis diagram 3)can be produced in the same fashion.

R₁ in general formula 1 preferably denotes an alkyl or an alkoxy groupwith between 1 and 7 C-atoms. They are preferably unbranched.

R₂ in general formula 1 preferably denotes an alkyl or alkoxy group withbetween 1 and 12 C-atoms, wherein the chains are preferably unbranched.

X in general formula 1 preferably denotes H or —CH₃, of which H isparticularly preferred.

The compounds of general formula 1 include the following preferredsub-formulae 1a, 1b and 1c, wherein in the formulae 1b and 1c thesignificances of X and R₁ are respectively independent of each other.

Thereof compounds of the formulae 1a and 1c are preferred.

Besides compounds of formula 1 the lubricant according to the inventioncan contain up to 80% of one or more additives. Such additives can beknown lubricating oils such as mineral oils produced from crude oil orsynthetic oils (see Ullmann's Encyclopaedia of Industrial Chemistry, 5thEdition, Vol A15, page 423 ff) and the additives known in tribology suchas anti-wear substances, anti-oxidants or anti-seizure substances.

Within the invention those additives which as is known involve agrease-like consistency such as metal soaps or polymers also apply asadditives. The latter can act as gel-forming agents or can be present inthe form of finely distributed particles such as for example PTFE(polytetrafluoroethylene). Besides lubricating oils therefore thelubricants according to the invention also include lubricating greases.

It is generally known that aryl-substituted 1,3-diketones arepredominantly present in the tautomeric keto-enol form 1 in accordancewith the diagram:

Within the present invention all tautomeric forms which are present inequilibrium are attributed to the keto compounds of the generalformula 1. In the databanks such compounds are referred to in asimplifying fashion as 1,3-diketones and thus also in Example 1hereinafter. As is known metal compounds (metal complexes) are derivedfrom a keto-enol form. Those compounds are embraced by the presentinvention. Their general formula can be reproduced as follows:

wherein M^(m) is a m-valent metal atom and m is a number between 1 and4.

Thus the structural formula

can be specified for the zinc complex which can be produced from theketo compound from synthesis diagram 1.

Preferred metal compounds are those of lithium, magnesium, titanium,zirconium, chromium, molybdenum, manganese, iron, nickel, copper, zincand tin, of which those of lithium, magnesium and zinc are particularlypreferred. Those compounds are preferably produced by the acetate, theacetyl acetonate complex or an alcoholate of the metal in question beingheated with one or more compounds of formula 1 and by the acetic acidwhich is liberated in that respect or the acetyl acetone or the alcoholbeing evaporated. Those metal compounds produced from compounds of thegeneral formula 1 can be present in a dissolved form but also in theform of a solid body if the lubricant according to the invention is alubricating grease. If there are more than one compound of formula 1there can be metal compounds with different ligands. A proportion ofthose metal compounds deemed to be within the present invention is thatwhich is obtained when the compounds of formula 1 and possibly alsovolatile additives are removed from the lubricant by distillation at180° C. sump temperature under an adequate reduced pressure. The residuecomprises the metal compounds according to the invention which are moststable at the sump temperature, and possibly further non-volatileadditives. The distinction which is possibly necessary between the metalcompounds from the compounds of formula 1 and further non-volatileadditives is effected in accordance with generally known analyticalmethods. A distinction which is possibly necessary between compounds offormula 1 and other volatile additives is also effected in thedistillate.

The compounds of general formula 1 can be mixed with other componentswhich are usual in the lubrication art, by simple stirring at ambienttemperature.

The lubricant according to the invention contains between 20 and 99.9,preferably between 50 and 99.9 and quite preferably between 70 and 99.9%of compounds of general formula 1 and/or metal compounds produced fromthose compounds.

The lubricant according to the invention can advantageously be used inthe generally known machine bearings which as is known are divided intoplain bearings or rolling bearings. Particular advantages are achievedin the lubrication of plain bearings, more specifically those inmachines in the textile industry, for example in regard to the needleguides of sewing machines, but also for lubricating pistons ofhigh-speed internal combustion engines.

The following Examples are intended to describe the invention withoutlimiting it. Temperatures are specified in degrees Celsius hereinbeforeand hereinafter. Percentages denote percent by mass. Hz denotes theoscillation frequency in 1/s. Within the invention a coefficient offriction is deemed to be particularly low if a coefficient of frictionof ≦0.05 can be achieved therewith in the test arrangement described inExample 1, with the specified parameters.

Example 1

The compound produced in accordance with synthesis diagram 1,1-(4-ethylphenyl)-3-hexyl-1,3-propandion, has a melting point of −1° C.and above that temperature is an isotropic fluid with a kinematicviscosity of 11.7 mm/s² at 23° C. 0.2% of the anti-oxidant2,6-di-tert.-butyl-p-kresol was dissolved therein.

To demonstrate the attainability of particularly favorable coefficientsof friction in plain bearings that lubricant was investigated in areversing sliding wear contact (Tribometer SRV III, Optimol InstrumentsPrüftechnik GmbH, Munich). A drop of the lubricant was put on to a flatdisk of a diameter of 24 mm and a thickness of 7.9 mm. A cylinder of adiameter of 15 mm and a length of 22 mm was moved thereon (bothcomponents involved in the frictional relationship were of steel 100Cr6,corresponding to the Deutsche Industrie Norm DIN 51834) at 90° C. undera load of 50 N at 50 Hz and a stroke of 1 mm at an angle of 10° inparallel relationship with the axis of rotation of the cylinder. After 6hours of test duration the coefficient of friction had fallen frominitially 0.20 to below 0.005. That value was not exceeded up to thetime that measurement was broken off after 20 hours. For comparison:commercially available lubricants, with the same parameters in respectof measurement, have coefficients of friction of between 0.2 and 0.1.

Example 2

A lubricant (lubricating grease) produced from:

30% PTFE powder, 5 μm (Dr Tillwich GmbH, Horb) presents particularly lowcoefficients of friction in plain bearings.

Example 3

A lubricant comprising

80% paraffin oil, with a dynamic viscosity at 20° C. 100-145 mPa·s, CAS8012-95-1 presents particularly low coefficients of friction in plainbearings.

Example 4

A lubricant comprising

25% paraffin oil, with a dynamic viscosity at 20° C. 100-145 mPa·s, CAS8012-95-1 presents particularly low coefficients of friction in plainbearings.

Example 5

are brought together and heated for 2 hours with agitation in a vacuumof 10 mbar at 120° C. The lubricant freed of ethanol (a lubricatinggrease) is of the composition

It presents particularly low coefficients of friction in plain bearings.

1-5. (canceled)
 6. A lubricant containing between 20 and 99.9% by massof one or more compounds of the general formula 1

wherein X denotes H, F, Cl, —CH₃, —C₂H₅, —OCH₃, R₁ respectively denoteindependently of each other H, an alkyl residue having a total ofbetween 1 and 18 C-atoms, in which also one or two non-adjacent CH₂groups can be replaced by —O—, —S— or —CO— and two adjacent CH₂ groupscan be replaced by —COO— or —OOC—, R₂ respectively denote independentlyof each other an alkyl residue having a total of between 1 and 18C-atoms, in which also one or two non-adjacent CH₂ groups can bereplaced by —O—, —S— and two non-adjacent CH₂ groups can be replaced by—COO— or —OOC—, or the residue

with the above-specified significances for X and R₁ and wherein n is anumber between zero and 12 and q is zero or
 1. 7. A lubricant as setforth in claim 6 wherein it contains between 50 and 99.9% by mass of oneor more compounds selected from the keto compounds of general formula 1.8. A lubricant as set forth in claim 6 wherein it contains between 70and 99.9% by mass of one or more compounds selected from the ketocompounds of general formula
 1. 9. A method for reducing frictionallosses between mutually moved solid bodies comprising interposing acompound according to claim 6 between the solid bodies.
 10. A method forreducing frictional losses between mutually moved solid bodiescomprising interposing a compound according to claim 7 between the solidbodies.
 11. A method for reducing frictional losses between mutuallymoved solid bodies comprising interposing a compound according to claim8 between the solid bodies.
 12. A bearing containing a lubricantaccording to claim
 6. 13. A bearing containing a lubricant according toclaim
 7. 14. A bearing containing a lubricant according to claim 8.